The present invention generally relates to the art of electrochemical energy, and more particularly, to an electrode assembly, electrochemical cells in which the electrode assembly is used, and a method for making the electrode assembly.
Batteries or electrochemical cells are typically volumetrically constrained systems that cannot exceed the available volume of the battery case. The size and resulting volume of the battery case are dictated by the space requirements available for the particular application. The components that make up a battery, namely, the cathode electrode, the anode electrode, the separator, the current collectors, and the electrolyte all have to fit into the limited space defined by the battery case. Therefore, the arrangement of the components impacts on the amount of active electrode material that can be fit into the case and the ease of manufacturing the unit.
Some typical electrode assemblies include the xe2x80x9cZxe2x80x9d folded electrode assembly that is disclosed in U.S. Pat. No. 3,663,721 to Blondel et al. In the xe2x80x9cZxe2x80x9d folded electrode, a unitary and continuous lithium anode is folded back and forth in a zigzag fashion. The length of the individual folds determines the width of the electrode assembly. Individual cathode plates are positioned between pairs of the pleated anode electrode and electrically connected to one another. The design has some drawbacks, including the requirement that separate cathode plates be inserted between each pair of adjacent layers of anode electrode and the requirement that electrical connections be made between all of the inserted cathode plates. This arrangement increases the time and costs associated with manufacturing.
Another typical electrode assembly configuration is the xe2x80x9cjelly rollxe2x80x9d design in which the anode electrode, the cathode electrode, and the separator are overlaid with respect to each other and coiled up. Such an electrode configuration is desirable because the continuous anode and cathode electrodes require a minimal number of mechanical connections to their respective terminal leads, and the jelly roll assembly is generally recognized as preferred for high discharge and current pulse applications. However, in some applications, a cylindrically shaped electrode assembly is not desired because of other factors, such as the shape of the battery case.
U.S. Pat. No. 4,761,352 to Bakos et al. discloses yet another electrode assembly design comprising an accordion folded electrode assembly with unitary members for both the anode and cathode strips. The cathode strip is approximately half the length of the anode strip, and the anode strip is folded over the cathode strip to xe2x80x9csandwichxe2x80x9d the cathode between two layers of the anode. The resulting form is then manually folded in an alternating series of xe2x80x9cVxe2x80x9d folds (best shown in FIG. 4 of the patent). However, that design provides some undesirable gaps which reduce the volumetric density of the electrochemically active materials.
What is needed is an improved multi-layer, folded electrode assembly design for high energy devices that includes many of the desirable features of the jelly roll design, such as unitary anode and cathode electrodes.
The present invention fills the above-described need by providing an electrochemical cell comprising an electrode assembly in which the electrodes are wound together in a bi-directional fashion, yielding a high energy density cell with low internal impedance. The anode and cathode electrodes are arranged in the cell in such a fashion that provides efficient utilization of the active components. The resultant wound assembly is configured such that it can be conveniently packaged in either a cylindrical or prismatic housing.
In one embodiment of the electrochemical cell, the electrodes are provided as two anode assemblies and one cathode assembly configured such that each anode is positioned on either side of the cathode assembly, and extending in opposing directions. At the center most portion of the assembly there is an overlap of anodes. This assembly is then wound about the overlapping region in a bi-directional fashion. The resultant assembly produces a wound cell stack configuration with a uniform contact of anode and cathode, such that the cell is balanced electrochemically and provides for optimum volume utilization within the battery enclosure. Each anode has one or more tabs that can be welded to the case. Alternately, two cathode assemblies can be paired with one anode assembly, with a resultant cathode tab welded to the case. In both of the above configurations, the opposite electrode may contain one or more tabs which are then electrically connected to the battery feedthrough pin.
An alternate embodiment of this invention provides for an anode electrode and a cathode electrode, wherein the electrodes are slotted. The electrodes are inserted, one into the other, essentially forming an xe2x80x9cXxe2x80x9d. Upon collapsing the electrodes, a variation of the above-described invention is obtained wherein the anode is approximately equally disposed on opposite sides of the cathode, radiating outwardly from its midportion. This assembly is then wound from the center, resulting in a preferred cell stack assembly. This configuration provides for the additional advantage of having the anode registered to the cathode, and mitigates the need for aligning two distinct anodes to the cathode.
Other features and advantages of the present invention will become apparent upon reading the following detailed description of embodiments of the invention, when taken in conjunction with the accompanying drawings and the appended claims.